Layer the cabbage and onion alternately in a large glass or ceramic bowl.
In a medium saucepan, combine the vinegar with the oil, sugar, chicken stock, salt, dry mustard and celery seeds. Bring to a boil, then pour the mixture over the cabbage and onion. Do not mix.
Let the slaw marinate in the refrigerator for 6 to 8 hours or overnight.Toss before serving.